File extension

.zstd

Zstandard (zstd) compressed data

.zst files are Zstandard-compressed streams: a modern lossless compressor offering a wide speed/ratio range, fast decompression, and trained dictionaries, increasingly a default in systems and packaging.

Known meanings

Formats and reference material for .zstd

Zstandard (zstd) compressed data

Modern fast lossless compression format with tunable levels and dictionary support

  • archive
  • Meta (Yann Collet) / IETF
Open link

Details

Format notes

Zstandard (zstd)

Zstandard is a modern lossless compression format, originally developed at Facebook (Meta) by Yann Collet, the author of LZ4. Its design goal is to provide a very wide range of compression levels — from very fast (competitive with LZ4) to high ratio (competitive with or better than gzip and, at high levels, approaching xz) — while keeping decompression consistently fast regardless of the level used. That flexibility has made it a common default in Linux distributions, package managers, file systems, and network protocols.

A .zst stream stores data compressed with an LZ77-style match finder combined with a fast entropy stage (finite state entropy and Huffman coding), framed with a magic number, optional content-size and checksum fields, and block structure. A standout feature is dictionary compression: zstd can be trained on a corpus of small, similar files to build a dictionary that dramatically improves the ratio when compressing many small payloads — valuable for databases, logs, and RPC.

Use And Preservation Notes

Like gzip and bzip2, zstd compresses a stream rather than bundling files, so it is paired with tar (.tar.zst) for archives. It is standardized in RFC 8878, which supports its use as a durable, openly specified format; the reference implementation is widely available. The common media type is application/zstd.

Security Notes

Compressed data can expand greatly, so software decompressing untrusted .zst streams should cap output size and memory to resist decompression bombs, and should be careful that any attacker-supplied dictionary is handled safely.

Further Reading

  • Zstandard home page: https://facebook.github.io/zstd/
  • RFC 8878 (Zstandard Compression): https://datatracker.ietf.org/doc/html/rfc8878